Support absolute path generation

[Dovizu]

Services such as Mailchimp does not support xml:base property, it’d be great to add absolute path support to the plugin.

[jekyllbot]

This issue has been automatically marked as stale because it has not been commented on for at least two months.

The resources of the Jekyll team are limited, and so we are asking for your help.

If this is a bug and you can still reproduce this error on the master branch, please reply with all of the information you have about it in order to keep the issue open.

If this is a feature request, please consider whether it can be accomplished in another way. If it cannot, please elaborate on why it is core to this project and why you feel more than 80% of users would find this beneficial.

This issue will automatically be closed in two months if no further activity occurs. Thank you for all your contributions.